Among alkoxysilanes, for instance trialkoxysilanes are used as silane coupling agents or the like for surface modification of inorganic materials, while tetraalkoxysilanes are widely used as starting materials of silica, zeolites, ceramics and organic/inorganic hybrid materials, according to sol-gel methods. Silanes substituted with organic groups or hydrogen atoms are functional chemicals that are used as reagents for precise synthesis, and as synthesis intermediates, in pharmaceuticals, agrichemicals, electronic materials and the like.
Ethoxy groups or methoxy groups are often used as the alkoxy groups in alkoxysilanes, but in recent years attention has been devoted to alkoxysilanes in which some or all the ethoxy groups or methoxy groups are substituted by other alkoxy groups, for the purpose of controlling the reactivity of the alkoxysilanes, or imparting functionality to the latter.
Catalysts such as acids and bases have been conventionally used to conduct reactions in which silanes having ethoxy groups or the like are caused to react with alcohols, to substitute the ethoxy groups or the like by alkoxy groups. Acid or base catalysts that have been used thus far include, for instance, trichloroacetic acid, piperidine or the like (Non-Patent Literature 1). Examples have also been reported in which halogen compounds, such as iodine or iodine bromide, are used as catalysts (Non-Patent Literature 2). Other instances have been reported where metallic sodium is used in reactions of tetramethoxysilane and di- or triethoxysilane (Non-Patent Literature 3 to 5). Also, examples are known where reactions of tetramethoxysilane, methyltrimethoxysilane and the like are conducted using organic or inorganic solid catalysts (Non-Patent Literature 6, Patent Literature 1 to 4).
However, these methods have the following problems: (1) when the catalyst is a liquid-state catalyst or is soluble in a solution, for instance as in the case of trichloroacetic acid or piperidine, separation and recovery of the catalyst after the reaction is not easy; (2) when the catalyst comprises iodine, the latter is not easy to handle easily due to the corrosive character of iodine; (3) when sodium is the catalyst, the latter is not easy to handle safely, since sodium is sensitive to moisture or the like; (4) it is ordinarily difficult to selectively make just some ethoxy groups or methoxy groups, in a plurality thereof, into other alkoxy groups; and (5) in the case of solid catalysts, the reaction system is a heterogeneous system, and, accordingly, reactions are slow and require a long reaction time, depending on the type of starting materials and reaction conditions. A demand arose thus for more industrially advantageous methods.
Among conventional methods, those that rely on inorganic solid catalysts are found to be superior to methods relying on organic solid catalyst as regards for instance the thermal stability and durability of the catalyst. However, specific usage examples known in the art, in the production reactions that utilize specific starting materials, include just calcium oxide, silica-alumina N-633HN (by Nikki Chemical Co., Ltd.), niobic acid, activated clay, protonated Y zeolites and thallium oxide (Examples 2, 4, 5 and 6 in Patent Literature 2, Examples 4 and 5 in Patent Literature 3). These examples are problematic in that the starting silane is used in excess with respect to the alcohol, and the yield of the generated silanes (total of mono-, di- and/or trisubstituted silane) with respect to the starting silane is often low (yields of about 10%, about 12%, about 12% and about 10%, respectively, in Examples 2, 4, 5 and 6 of Patent Literature 2, and yield of about 16% in Example 5 of Patent Literature 3), or are problematic in that the selectivity for the monosubstituted product, in which only some methoxy groups of the starting material are substituted by alkoxy groups, is not high (ratios of the mono-, di- and trisubstituted products of 57.3:35.6:7.1 in Example 4 of Patent Literature 3). More effective inorganic solid catalysts were thus desirable. Although there is no detailed explanation concerning how to obtain protonated Y-type zeolites, used as described above, it is deemed that the silica/alumina ratio (SiO2/Al2O3 ratio) is 136/(56×0.5)=4.86, in the light of the disclosure “Bronsted acid sites (H+) were generated through substitution of Na ions by NH4+, on the surface of Y-type zeolite (Na56(AlO2)56(SiO2)136.nH2O) particles, and desorption of NH3 through a heating treatment at 300° C.” (Patent Literature 3, paragraph [0038], table 2, footnote 2). Nothing, however, is disclosed regarding Y-type zeolites having other silica/alumina ratios, or regarding zeolites of structures other than Y type, while the effectiveness of the foregoing zeolites is likewise unknown.    Non-Patent Literature 1: J. Gen. Chem. USSR, 37, 2630-2631 (1967)    Non-Patent Literature 2: Bull. Chem. Soc. Jpn., 55, 2973-2975 (1982)    Non-Patent Literature 3: Chem. Ber., 80, 163-164 (1947)    Non-Patent Literature 4: Acta Chem. Scand., 8, 898-900 (1954)    Non-Patent Literature 5: J. Organomet. Chem., 25, 359-365 (1970)    Non-Patent Literature 6: Bull. Chem. Soc. Jpn., 61, 4087-4092 (1988)    Patent Literature 1: Japanese Patent Application Publication No. H4-295486    Patent Literature 2: Japanese Patent Application Publication No. H5-255348    Patent Literature 3: Japanese Patent Application Publication No. H5-255349    Patent Literature 4: Japanese Patent Application Publication No. 2004-269465